NAME

isakmpd.policy - policy configuration file for isakmpd

DESCRIPTION

isakmpd.policy is the policy configuration file for the isakmpd daemon
managing security association and key management for the ipsec(4) layer
of the kernel’s networking stack.
The isakmpd(8) daemon (also known as IKE, for Internet Key Exchange) is
used when two systems need to automatically set up a pair of Security
Associations (SAs) for securely communicating using IPsec. IKE operates
in two stages:
In the first stage (Main or Identity Protection Mode), the two IKE
daemons establish a secure link between themselves, fully authenticating
each other and establishing key material for encrypting/authenticating
future communications between them. This step is typically only
performed once for every pair of IKE daemons.
In the second stage (also called Quick Mode), the two IKE daemons create
the pair of SAs for the parties that wish to communicate using IPsec.
These parties may be the hosts the IKE daemons run on, a host and a
network behind a firewall, or two networks behind their respective
firewalls. At this stage, the exact parameters of the SAs (e.g.,
algorithms to use, encapsulation mode, lifetime) and the identities of
the communicating parties (hosts, networks, etc.) are specified. The
reason for the existence of Quick Mode is to allow for fast SA setup,
once the more heavy-weight Main Mode has been completed. Generally,
Quick Mode uses the key material derived from Main Mode to provide keys
to the IPsec transforms to be used. Alternatively, a new Diffie-Hellman
computation may be performed (significantly slowing down the exchange,
but at the same time providing Perfect Forward Secrecy (PFS)). Briefly,
this means that even should an attacker manage to break long-term keys
used in other sessions (or, specifically, if an attacker breaks the
Diffie-Hellman exchange performed during Main Mode), they will not be
able to decrypt this traffic. Normally, no PFS is provided (the key
material used by the IPsec SAs established as a result of this exchange
will be derived from the key material of the Main Mode exchange),
allowing for a faster Quick Mode exchange (no public key computations).
IKE proposals are "suggestions" by the initiator of an exchange to the
responder as to what protocols and attributes should be used on a class
of packets. For example, a given exchange may ask for ESP with 3DES and
MD5 and AH with SHA1 (applied successively on the same packet), or just
ESP with Blowfish and RIPEMD-160. The responder examines the proposals
and determines which of them are acceptable, according to policy and any
credentials.
The following paragraphs assume some knowledge of the contents of the
keynote(4) and keynote(5) man pages.
In the KeyNote policy model for IPsec, no distinction is currently made
based on the ordering of AH and ESP in the packet. Should this change in
the future, an appropriate attribute (see below) will be added.
The goal of security policy for IKE is thus to determine, based on local
policy (provided in the isakmpd.policy file), credentials provided during
the IKE exchanges (or obtained through other means), the SA attributes
proposed during the exchange, and perhaps other (side-channel)
information, whether a pair of SAs should be installed in the system (in
fact, whether both the IPsec SAs and the flows should be installed). For
each proposal suggested by or to the remote IKE daemon, the KeyNote
system is consulted as to whether the proposal is acceptable based on
local policy (contained in isakmpd.policy, in the form of policy
assertions) and remote credentials (e.g., KeyNote credentials or X509
certificates provided by the remote IKE daemon).
isakmpd.policy is simply a flat ascii(7) file containing KeyNote policy
assertions, separated by blank lines (note that KeyNote assertions may
not contain blank lines). isakmpd.policy is read when isakmpd(8) is
first started, and every time it receives a SIGHUP signal. The new
policies read will be used for all new Phase 2 (IPsec) SAs established
from that point on (even if the associated Phase 1 SA was already
established when the new policies were loaded). The policy change will
not affect already established Phase 2 SAs.
For more details on KeyNote assertion format, please see keynote(5).
Briefly, KeyNote policy assertions used in IKE have the following
characteristics:
· The Authorizer field is typically "POLICY" (but see the examples
below, for use of policy delegation).
· The Licensees field can be an expression of passphrases used for
authentication of the Main Mode exchanges, and/or public keys
(typically, X509 certificates), and/or X509 distinguished names.
· The Conditions field contains an expression of attributes from the
IPsec policy action set (see below as well as the keynote syntax man
page for more details).
· The ordered return-values set for IPsec policy is "false, true".
For an explanation of these fields and their semantics, see keynote(5).
For example, the following policy assertion:
Authorizer: "POLICY"
Licensees: "passphrase:foobar" || "x509-base64:abcd==" ||
"passphrase-md5-hex:3858f62230ac3c915f300c664312c63f" ||
"passphrase-sha1-hex:8843d7f92416211de9ebb963ff4ce28125932878"
Conditions: app_domain == "IPsec policy" && esp_present == "yes"
&& esp_enc_alg != "null" -> "true";
says that any proposal from a remote host that authenticates using the
passphrase "foobar" or the public key contained in the X509 certificate
encoded as "abcd==" will be accepted, as long as it contains ESP with a
non-null algorithm (i.e., the packet will be encrypted). The last two
authorizers are the MD5 and SHA1 hashes respectively of the passphrase
"foobar". This form may be used instead of the "passphrase:..." one to
protect the passphrase as included in the policy file (or as distributed
in a signed credential).
The following policy assertion:
Authorizer: "POLICY"
Licensees: "DN:/CN=CA Certificate"
Conditions: app_domain == "IPsec policy" && esp_present == "yes"
&& esp_enc_alg != "null" -> "true";
is similar to the previous one, but instead of including a complete X509
credential in the Licensees field, only the X509 certificate’s Subject
Canonical Name needs to be specified (note that the "DN:" prefix is
necessary).
KeyNote credentials have the same format as policy assertions, with one
difference: the Authorizer field always contains a public key, and the
assertion is signed (and thus its integrity can be cryptographically
verified). Credentials are used to build chains of delegation of
authority. They can be exchanged during an IKE exchange, or can be
retrieved through some out-of-band mechanism (no such mechanism is
currently supported in this implementation however). See isakmpd.conf(5)
on how to specify what credentials to send in an IKE exchange.
Passphrases that appear in the Licensees field are encoded as the string
"passphrase:", followed by the passphrase itself (case-sensitive).
Alternatively (and preferably), they may be encoded using the
"passphrase-md5-hex:" or "passphrase-sha1-hex:" prefixes, followed by the
md5(1) or sha1(1) hash of the passphrase itself, encoded as a hexadecimal
string (using lower-case letters only).
When X509-based authentication is performed in Main Mode, any X509
certificates received from the remote IKE daemon are converted to very
simple KeyNote credentials. The conversion is straightforward: the
issuer of the X509 certificate becomes the Authorizer of the KeyNote
credential, the subject becomes the only Licensees entry, while the
Conditions field simply asserts that the credential is only valid for
"IPsec policy" use (see the app_domain action attribute below).
Similarly, any X509 CA certificates present in the directory pointed to
by the appropriate isakmpd.conf(5) entry, are converted to such pseudo-
credentials. This allows one to write KeyNote policies that delegate
specific authority to CAs (and the keys those CAs certify, recursively).
For more details on KeyNote assertion format, see keynote(5).
Information about the proposals, the identity of the remote IKE daemon,
the packet classes to be protected, etc. are encoded in what is called an
action set. The action set is composed of name-value attributes, similar
in some ways to shell environment variables. These values are
initialized by isakmpd before each query to the KeyNote system, and can
be tested against in the Conditions field of assertions. See keynote(4)
and keynote(5) for more details on the format and semantics of the
Conditions field.
Note that assertions and credentials can make references to non-existent
attributes without catastrophic failures (access may be denied, depending
on the overall structure, but will not be accidentally granted). One
reason for credentials referencing non-existent attributes is that they
were defined within a specific implementation or network only.
In the following attribute set, IPv4 addresses are encoded as ASCII
strings in the usual dotted-quad format. However, all quads are three
digits long. For example, the IPv4 address 10.128.1.12 would be encoded
as 010.128.001.012. Similarly, IPv6 addresses are encoded in the
standard x:x:x:x:x:x:x:x format, where the ’x’s are the hexadecimal
values of the eight 16-bit pieces of the address. All ’x’s are four
digits long. For example, the address 1080:0:12:0:8:800:200C:417A would
be encoded as 1080:0000:0012:0000:0008:0800:200C:417A.
The following attributes are currently defined:
app_domain
Always set to IPsecpolicy.
doi Always set to ipsec.
initiator
Set to yes if the local daemon is initiating the Phase 2 SA, no
otherwise.
phase_1 Set to aggressive if aggressive mode was used to establish the
Phase 1 SA, or main if main mode was used instead.
pfs Set to yes if a Diffie-Hellman exchange will be performed during
this Quick Mode, no otherwise.
ah_present, esp_present, comp_present
Set to yes if an AH, ESP, or compression proposal was received
respectively, no otherwise.
ah_hash_alg
One of md5, sha, ripemd, sha2-256, sha2-385, sha2-512, or des,
based on the hash algorithm specified in the AH proposal. This
attribute describes the generic transform to be used in the AH
authentication.
esp_enc_alg
One of des, des-iv64, 3des, rc4, idea, cast, blowfish, 3idea,
des-iv32, rc4, null, or aes, based on the encryption algorithm
specified in the ESP proposal.
comp_alg
One of oui, deflate, lzs, or v42bis, based on the compression
algorithm specified in the compression proposal.
ah_auth_alg
One of hmac-md5, hmac-sha, des-mac, kpdk, hmac-sha2-256,
hmac-sha2-385, hmac-sha2-512, or hmac-ripemd. based on the
authentication method specified in the AH proposal.
esp_auth_alg
One of hmac-md5, hmac-sha, des-mac, kpdk, hmac-sha2-256,
hmac-sha2-385, hmac-sha2-512, or hmac-ripemd based on the
authentication method specified in the ESP proposal.
ah_life_seconds, esp_life_seconds, comp_life_seconds
Set to the lifetime of the AH, ESP, and compression proposal, in
seconds. If no lifetime was proposed for the corresponding
protocol (e.g., there was no proposal for AH), the corresponding
attribute will be set to zero.
ah_life_kbytes, esp_life_kbytes, comp_life_kbytes
Set to the lifetime of the AH, ESP, and compression proposal, in
kbytes of traffic. If no lifetime was proposed for the
corresponding protocol (e.g., there was no proposal for AH), the
corresponding attribute will be set to zero.
ah_encapsulation, esp_encapsulation, comp_encapsulation
Set to tunnel or transport, based on the AH, ESP, and
compression proposal.
ah_ecn, esp_ecn, comp_ecn
Set to yes or no, based on whether ECN was requested for the
IPsec tunnel.
comp_dict_size
Specifies the log2 maximum size of the dictionary, according to
the compression proposal.
comp_private_alg
Set to an integer specifying the private algorithm in use,
according to the compression proposal.
ah_key_length, esp_key_length
The number of key bits to be used by the authentication and
encryption algorithms respectively (for variable key-size
algorithms).
ah_key_rounds, esp_key length
The number of rounds of the authentication and encryption
algorithms respectively (for variable round algorithms).
ah_group_desc, esp_group_desc, comp_group_desc
The Diffie-Hellman group identifier from the AH, ESP, and
compression proposal, used for PFS during Quick Mode (see the
pfs attribute above). If more than one of these attributes are
set to a value other than zero, they should have the same value
(in valid IKE proposals). Valid values are 1 (768-bit MODP), 2
(1024-bit MODP), 3 (155-bit EC), 4 (185-bit EC), and 5 (1536-bit
MODP).
phase1_group_desc
The Diffie-Hellman group identifier used in IKE Phase 1. Takes
the same values as ah_group_desc.
remote_filter_type, local_filter_type, remote_id_type
Set to IPv4address, IPv4range, IPv4subnet, IPv6address, IPv6range, IPv6subnet, FQDN, UserFQDN, ASN1DN, ASN1GN, or KeyID, based on the Quick Mode Initiator ID, Quick Mode Responder
ID, and Main Mode peer ID respectively.
remote_filter_addr_upper, local_filter_addr_upper, remote_id_addr_upper
When the corresponding filter_type is IPv4address or IPv6address, these contain the respective address. For IPv4range
or IPv6range, they contain the upper end of the address range.
For IPv4subnet or IPv6subnet, they contain the highest address
in the specified subnet.
remote_filter_addr_lower, local_filter_addr_lower, remote_id_addr_lower
When the corresponding filter_type is IPv4address or IPv6address, these contain the respective address. For IPv4range
or IPv6range, these contain the lower end of the address range.
For IPv4subnet or IPv6subnet, these contain the lowest address
in the specified subnet.
remote_filter, local_filter, remote_id
When the corresponding filter_type specifies an address range or
subnet, these are set to the upper and lower part of the address
space separated by a dash (’-’) character (if the type specifies
a single address, they are set to that address).
For FQDN and User FQDN types, these are set to the respective
string. For Key ID, these are set to the hexadecimal
representation of the associated byte string (lower-case letters
used) if the Key ID payload contains non-printable characters.
Otherwise, they are set to the respective string.
For ASN1 DN, these are set to the text encoding of the
Distinguished Name in the payload sent or received. The format
is the same as that used in the Licensees field.
remote_filter_port, local_filter_port, remote_id_port
Set to the transport protocol port.
remote_filter_proto, local_filter_proto, remote_id_proto
Set to etherip, tcp, udp, or the transport protocol number,
depending on the transport protocol set in the IDci, IDcr, and
Main Mode peer ID respectively.
remote_negotiation_address
Set to the IPv4 or IPv6 address of the remote IKE daemon.
local_negotiation_address
Set to the IPv4 or IPv6 address of the local interface used by
the local IKE daemon for this exchange.
GMTTimeOfDay
Set to the UTC date/time, in YYYYMMDDHHmmSS format.
LocalTimeOfDay
Set to the local date/time, in YYYYMMDDHHmmSS format.